Urban energy system planning from wide area network perspective

Abstract

The urban energy system, consisting of multiple subsystems ranging from energy production, transformation, transmission, storage, to consumption, plays a critical role in the national and regional energy network. Due to its complexity, to optimize the urban energy system from multiple aspects and scales are necessary. Currently, a large number of urban energy planning studies have focused on optimization methods and theories targeting integrated energy systems at community scale. Several energy system optimization models have also been developed based on different technical ideas. However, from a wide area perspective, the integrated community energy system represents a small local network in the overall urban energy system network. Neglecting the mutual interaction between the local network and wide area network can result in a severe segmentation issue and low energy efficiency. But it is impractical to take into account each end-user individually during the optimization of the urban energy system, since the construction activities involved in the energy demand-supply planning cover a wide range of aspects and a long period. Therefore, the coordination between the local and overall energy networks requires in-depth exploration of the incidence relation among them. In this study, the formation of the urban energy demand and supply chains and the structure of urban energy flow network being described by tracking the energy flow from the end-users to the energy source extraction. Based on the concepts of primary energy market and secondary energy market in urban regions and local areas, respectively, the differences and connections between energy flow networks from the supply and demand sides have been discussed. Subsequently, a two-layer four-stage urban energy planning system was proposed based on the planning objects and contents. Furthermore, the typical nested and parallel relations between different local networks were proposed based on energy transformations and dissipation flows. From the structure investigation of urban energy network, such conclusions are listed as flows: (1) The overall energy flow network can be divided into two independent layers. The first network is responsible for the optimization of energy extraction from sources and the trade of energy between difference cities. The formation and evolution of the first network is dominated by the price mechanism of primary energy. The second network is focused on the local distribution of different energy resources (e.g., electricity, gas) based on the demand, and its formation and evolution are governed by the urban municipal plan (local regulations or policies). These two energy markets are independent systems interconnected by the energy price and the demand-supply information. (2) The topology of the primary energy market is flat, which indicated that there is no apparent monopoly of information or controlling center in the market. Therefore, the trading flow of energy resources forms naturally under the influence of price mechanisms. The secondary energy market is, however, controlled by an information center where the centralized processing of the scattered end-user information leads to a highly controlled limited energy market. (3) In order to integrate the different urban energy sources into an overall energy planning scheme, the current energy distribution situation with fixed beneficiaries should be changed drastically. However, there is a lack of leadership and motivation to drive such change. (4) The cost of electricity and gas used for cooling and heating in urban areas has a high impact on the secondary energy planning. An improper choice of energy price system will adversely affect the process of reducing energy consumption. (5) Establishing a smart energy supply system in urban areas requires a synergetic integration of information systems for both energy and social-economic systems. However, currently there is no study on the mutual interaction between energy systems and social-economic systems.